1. Field of the Invention
The present invention relates to an automatic position controlling apparatus. More specifically, the present invention relates to an improved follow-up control in a position controlling apparatus using a playback system of a point-to-point type.
2. Description of the Prior Art
FIG. 1 is a perspective view showing one example of an automatic cutting apparatus which constitutes the background of the invention and wherein the present invention can be advantageously employed. The automatic cutting robot comprises a base 101 extending in a horizontal direction, i.e. an X axis direction and a first moving member 102 is borne on the base 101 to be movable in the X axis direction. The moving member 102 is integrally provided with a column 103 extending upright and a second moving member 104 is provided so as to be penetrated by the column 103 and to be movable in the vertical direction, i.e. in a Z axis direction. A beam 105 is further supported by the moving member 104 to be movable in the direction orthogonal to the X axis direction and the Z axis direction, i.e. in a Y axis direction. A shaft 106 is supported at the tip end of the beam 105 at the axis 106a extending in the same direction as the Z axis direction, the rotation angle of the shaft 106 being denoted by .phi.. A fixture 108 or a cutting torch 109 is supported at the lower end of the shaft 106 by means of a balanced link means 107. The balanced link means 107 is structured such that the position of a working point 109a of the torch 109 may be at a predetermined point on the axis 106a even if an attitude angle .psi. of the torch 109 is variable and even in any value of the angle .psi.. The fixture 108 is adapted such that the torch 109 fixed thereto may be rotatable about the axis 108a, the rotational angle thereof being represented by .theta.. More specifically, the cutting robot 100 shown in FIG. 1 has sixth degrees of freedom of X, Y, Z, .phi., .psi. and .theta., and is additionally provided with driving systems for position control thereof and a control means such as a computer. A workpiece 200 is cut along a cutting line 201 of the workpiece 200 by means of the torch 109.
With a conventional robot using a playback system, a moving locus (path) of a means being controlled is prepared using linear or arcuate interpolation of the taught passing points, whereupon commanded position information of the means being controlled is obtained. According to such conventional approach, in addition to a problem of connection of paths, another problem was involved that the speed of paths and accuracy of positions are poor due to inertia and a response characteristic in operation of the means being controlled.
On the other hand, according to a robot of a continuous path system, such as disclosed in Japanese Patent Laying Open Gazette No. 31456/1976, it has been proposed that a new target value associated with a load or inertia of a driving system is evaluated based on the taught target values, whereby a follow-up control is achieved. However, the above described prior art can not be applied to a robot of a point-to-point type to which the present invention is directed. The reason is that in the case of a continuous path type the above described target values are represented as a function of time, whereas in the case of a point-to-point type the position information of the points to which the positions should be controlled and the speed information of the movement being controlled have been taught and therefore the target values have not been represented as a function of time. Accordingly, it is desired that there is provided a position controlling apparatus suited for a robot of a point-to-point type, which is implemented from a point of view entirely different from the above described prior art and that is capable of achieving a control with high speed and with high accuracy.